The simplest form of array spectrophotometer utilizes a single fixed diffraction grating dispersing a spectrum over the length of a photodiode array (PDA) located in the exit focal plane. However, unless only a short wavelength range is covered such a system suffers from excessive stray light errors as well as second order errors, particularly if more than one source is used, eg. a tungsten lamp for the visible range and a deuterium arc lamp for the UV range. Prior art systems try to eliminate such errors by using order sorting or energy correction filters inserted sequentially into the source beam. This, however, requires a complex of expensive multiple filters and moving parts which act at slow speeds and produce spikes and offsets at transition points on the scan data.
This invention discloses a combination of simple optical means associated with a novel computer control routine which overcomes the defects cited above for prior art systems.
It is an object of this invention to provide an improved array spectrophotometer using a single fixed diffraction grating as dispersive means.
It is a further object to provide more than one energy source, each of these sources providing radiation over an effective part of the total wavelength range; the sum of these parts covering the total range.
It is a further object to scan the wavelength range more than once using a different source during each scan, and subsequently by computer means to combine the data thus obtained to give complete range coverage.
It is an objective of the computer data processing to correct for stray light associated with each source over the effective range of said source.
It is a further objective to switch said sources optically by simple computer controlled means without extinguishing said sources.
It is also an objective to utilize a fixed optical filter to provide rejection of second order reference stray light in effective combination with said computer controlled switching means.
It is yet a further objective to provide computer controlled spectral response flattening means for said sources as required to avoid response overload of the photocell array.
It is also an objective to provide computer combination of selected ranges of each scan appropriate to each source, and rejection of the rest of each scan so that only the effective range of each source appears in the final data.
It is also a further objective to smooth the data by computer means at the transition from one source to another so that no transition spikes, offsets or other artifacts will appear in the combined scan.